Author Topic: RFM69HW range test!  (Read 58792 times)

CaptainJack

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Re: RFM69HW range test!
« Reply #30 on: July 09, 2014, 08:51:34 AM »
Philip,

thanks for your replies, it took me some time to get to my rfm69 again. I will build a setup with just a piece of wire as antenna to see how that works out. As soon as I have results I'll post them together with register settings.

I will have to look into that spectrum analyzer. What I have learnt is mostly that there is still much to learn about RF. I'll try and pick up a good book about it for the summer.

Cheers,

Jack

hneiraf

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Re: RFM69HW range test!
« Reply #31 on: July 25, 2014, 09:51:49 PM »
Hi hdphilip,

You said this in a previous post: "I had it set at power level 29, max power would hang up the TX"

In my experience using both default bitrate (56k) and your low bitrate configuration(1.2k), using a simple wire antenna with 433mhz RFM69HW I get better results with powerlevel 31. But when I use a high gain antenna (a 80 cm antenna with 5.5dbi) then I get better results using powerlevel 29.

These are the antenna features:
Frequency Range(MHz):433+/-5
V.S.W.R:<=1.5
Input Impedance(OHM):50
Max-power(W):10
Gain(dBi):5.5
Polarization:Vertical
Height(cm):80
Cable Length(cm):300
Weight(kg):0.5
Connector Type:SMA

Can you explain me/us why that happens, basically when to use powerlevel 31 and when to use powerlevel 29? in order to get better results?
I mean, you are the expert, and I would like to know when to reduce the powerlevel and when to increase it, more in deep than just try and try walking and walking away as I do :D

Hope you can help us

Thank you in advance!

Hugo

hdphilip

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Re: RFM69HW range test!
« Reply #32 on: July 26, 2014, 07:06:52 PM »

Hugo,

let me try this again, my first reply got deleted cause my picture attachment was too large.................

things to consider when using the highest power:

 
Quote
The Duty Cycle of transmission at +20dBm is limited to 1%, with a maximum VSWR of 3:1 at antenna port, over the
standard operating range [-40;+85C].

if you were to upload a sketch could you damage the chip?

    I found my range suffered when i tried power level 31, not so much on the default bitrate, more so at slower bitrates. I don't have a power meter to measure the output, but maybe the slower bitrates are over driving the PA.


Would you  rather have a cleaner signal at a lower power, then a stronger, possible dirtier signal?
for instance, turning the volume on a television to 100% seldom makes the audio sounds better...

What kind of antenna is the 5.5 dB your using?

    I found all of those cheap ebay 433 MHz antennas were junk for long range, even though the SWR looked good on my sweep generator, their performance was poor.

Those bare "spring" antennas were ok. if you just don't have the space.

Philip

 
 
 
 




hdphilip

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Re: RFM69HW range test!
« Reply #33 on: July 26, 2014, 07:54:55 PM »
Hugo,

try some temp experiments,

set one of your unit outside in direct sunlight, and the other in the icebox, and compare rssi as the unit warms up from being in the icebox.

here's a few pictures.
Notice the ND TEMP of the unit outside and the temp of my display box (notice the frost on it) it shown on the LCD in yellow.

with temp compensation, I get "free db's worth of gain"

this is my "hybrid" moteino's, the outside unit has a small solar panel to keep the battery charged.

philip
« Last Edit: July 26, 2014, 07:58:55 PM by hdphilip »

griff

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Re: RFM69HW range test!
« Reply #34 on: July 07, 2015, 01:14:25 PM »
In 2013 Drae reported RFM69HW range test results of 540 meters. I also obtain about the same range. In the US, if you have an amateur radio license (a.k.a "ham radio"), you might check out my experience using a Moteino (RFM69HW) at  http://w5vwp.com/moteino.shtml. The web-page describes how I constructed a 4 watt 56kbps 433mhz Moteino transceiver for about $75 with a range of about 3 miles (5 km) to a mobile antenna.  I put firmware for the moteino on http://github.com/griff2/rfm69rptr. This firmware displays whatever you type on your keyboard to the screen of the "remote" computer, and vice versa.  The transceiver uses a Moteino plus a Chinese FSK 4 watt power amplifier ($53)I purchased on ebay.com.  To use this much power legally in the US, you must have a ham (or other) FCC license. For even longer range, try using directional antennas and/or the Down East Microwave (http://fwfvq.tehfm.servertrust.com/category-s/1814.htm) 433mhz 30 watt linear power amplifier, model 7025PA ($215).

Griff W5VWP

A_Christensen

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Re: RFM69HW range test!
« Reply #35 on: April 09, 2017, 09:15:34 AM »
Hi guys.  Hope to bring this old topic back to life.

We have tried to walk trough all the posts and change the cpp file to
bitrate   1200
RegFdev 2000
RegRxBw 0x19,0x56

When we go below 9600 baud.. it all just stop working.

Is there anyone out there that can be our hero and let us see a low baud working rfm69 cpp file. ?

We are running the RFM69HCW 433mhz.   and our goal is 3KM.

Dipoles are on their way.  But right now we are stuck at 300m. And we simply do not have any clue as to what settings could be wrong.

any help is greatly appreciated.

The RFM96 is a possibility. But the 10 x RFM69 we have bought for our demo, would be very nice getting to run. :)


perky

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Re: RFM69HW range test!
« Reply #36 on: April 09, 2017, 09:42:13 AM »
Useful reference for BR, Fdev and RxBw:
https://lowpowerlab.com/forum/rf-range-antennas-rfm69-library/definition-of-rxbw-with-rfm69/

From this the rules are (assuming you're not not using AFC):
1)  0.5 <= 2 * Fdev/BR <= 10    (modulation index, MI)
2)  BR < 2*RxBw     (bit rate)
3)  RxBw >=  Fdev + BR/2 + LOoffset (receiver bandwidth)
4)  Fdev + BR/2 < 500kHz  (maximum RxBw setting)

So at BR =1200, Fdev = 2000 you need RxBw >= 2600 + LOoffset.  However LOoffset can be quite high. At a nominal 20ppm (+/-10ppm) that can be 8.6kHz at 433MHz, but if you take into account temperature and drift it could be as high as +/-35ppm, or 70ppm for LOoffset. That's worst case and the crystals are better speced than that, but it's still much higher than your RxBw which you've set to 5.6kHz!

So I'd try setting RxBw to 31.3kHz, i.e. reg 0x19 set to 0x44.

Mark.
« Last Edit: April 09, 2017, 09:51:47 AM by perky »

A_Christensen

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Re: RFM69HW range test!
« Reply #37 on: April 09, 2017, 02:32:27 PM »
Awesome!
We will give it a go ASAP. Thank you for the explanation! We get smarter every day. I'll post our findings!

steve v

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Re: RFM69HW range test!
« Reply #38 on: April 10, 2017, 01:51:59 PM »
If your Local oscillator Offset is too high, you can try what I have been doing.

Simply manually type in a frequency offset to only One of the two devices.

I.e  set your  Moteino #1  to 433.000 Mhz and your Moteino #2   try  433.006, 433.003, 432.997,  432.994   chances are one of those 4 frequs will be closer than your original test and it will fit into the 5.6Khz RxBW

Perhaps someone could write a code loop to automatically scan through a range of Frequs and print the frequs that worked

Steve


A_Christensen

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Re: RFM69HW range test!
« Reply #39 on: April 10, 2017, 07:13:58 PM »
So we made the changes. But once again the entire communication stopped.
BR =1200,
Fdev = 2000
RxBw = ( reg 0x19 set to 0x44 )

We then by mistake loaded
BR =1200,
Fdev = 20000
RxBw = ( reg 0x19 set to 0x44 )

When we loaded the Fdev = 20000 it all lighted up like a Christmas tree.
Not completely understanding this. We are running 1200 bauds and communicating.

Can anyone teach me how Fdev works.?

Useful reference for BR, Fdev and RxBw:
https://lowpowerlab.com/forum/rf-range-antennas-rfm69-library/definition-of-rxbw-with-rfm69/

From this the rules are (assuming you're not not using AFC):
1)  0.5 <= 2 * Fdev/BR <= 10    (modulation index, MI)
2)  BR < 2*RxBw     (bit rate)
3)  RxBw >=  Fdev + BR/2 + LOoffset (receiver bandwidth)
4)  Fdev + BR/2 < 500kHz  (maximum RxBw setting)

So at BR =1200, Fdev = 2000 you need RxBw >= 2600 + LOoffset.  However LOoffset can be quite high. At a nominal 20ppm (+/-10ppm) that can be 8.6kHz at 433MHz, but if you take into account temperature and drift it could be as high as +/-35ppm, or 70ppm for LOoffset. That's worst case and the crystals are better speced than that, but it's still much higher than your RxBw which you've set to 5.6kHz!

So I'd try setting RxBw to 31.3kHz, i.e. reg 0x19 set to 0x44.

Mark.

joelucid

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Re: RFM69HW range test!
« Reply #40 on: April 11, 2017, 02:09:23 AM »
Quote
When we loaded the Fdev = 20000 it all lighted up like a Christmas tree.
Not completely understanding this. We are running 1200 bauds and communicating.

These radios can't tolerate a large relative frequency offset to frequency deviation. Over 30% and you can place radios right next to each other, they won't talk. To use narrow fdev you need to reduce the frequency offset between both nodes. You could use AFC (see datasheet) for example. However this isn't trivial to do. Look around, there have been threads about it.

LukaQ

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Re: RFM69HW range test!
« Reply #41 on: February 07, 2018, 04:40:45 PM »
To use narrow fdev you need to reduce the frequency offset between both nodes, how do you find out, what is that offset between nodes?
As it seems to me, you don't but you do compensate that with bandwidth.

let's say at 868MHz, LOoffset = 8.68k
BR = 1200
Fdev = 2000
RxBw >=  Fdev + BR/2 + LOoffset (receiver bandwidth) = 11.3k
Then if you set REG_RXBW to 20.8k or even 15.6k it should work right?

perky

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Re: RFM69HW range test!
« Reply #42 on: February 08, 2018, 06:54:30 AM »
I think those 'rules' may need some additional qualification.

At the transmitter there will be two modulation frequencies, FDEV either side of the transmitter carrier. At the reveiver those frequencies are (FDEV + LOoffset) and (FDEV - LOoffset) relative to the receiver's carrier. It appears that without AFC the radios stop receiving if there is a significant difference between these two deviations. Worst case is both these deviations could appear on the same side of the receiver carrier if LOoffset is large enough. So even though the receiver bandwidth is large enough to see both of those frequencies, the demodulator has trouble demodulating.

With AFC the receiver carrier frequency is adjusted to be the same as the transmitter carrier, but it requires a longer preamble. It does appear that even if both transmitted frequencies are on the same side of the receiver carrier the AFC is still capable of adjusting correctly (assuming of course the receiver bandwidth is large enough to capture them).

So what you saw when you increased FDEV is that the relative percentage difference of the two frequencies either side of the receiver carrier reduced to the point it started to work.

I think you're going to have to use AFC. It's not that complicated, you need to set RxBwAFC and have a longer preamble (which you can calculate from formulae in the datasheet). Once AFC is done it will then automatically use RxBw so that can be set significantly lower because LOoffset is no longer a factor, in other words subsequent reception has a higher signal to noise for more robust reception.

Mark.

LukaQ

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Re: RFM69HW range test!
« Reply #43 on: February 08, 2018, 09:15:52 AM »
I think those 'rules' may need some additional qualification.

At the transmitter there will be two modulation frequencies, FDEV either side of the transmitter carrier. At the reveiver those frequencies are (FDEV + LOoffset) and (FDEV - LOoffset) relative to the receiver's carrier. It appears that without AFC the radios stop receiving if there is a significant difference between these two deviations. Worst case is both these deviations could appear on the same side of the receiver carrier if LOoffset is large enough. So even though the receiver bandwidth is large enough to see both of those frequencies, the demodulator has trouble demodulating.

With AFC the receiver carrier frequency is adjusted to be the same as the transmitter carrier, but it requires a longer preamble. It does appear that even if both transmitted frequencies are on the same side of the receiver carrier the AFC is still capable of adjusting correctly (assuming of course the receiver bandwidth is large enough to capture them).

So what you saw when you increased FDEV is that the relative percentage difference of the two frequencies either side of the receiver carrier reduced to the point it started to work.

I think you're going to have to use AFC. It's not that complicated, you need to set RxBwAFC and have a longer preamble (which you can calculate from formulae in the datasheet). Once AFC is done it will then automatically use RxBw so that can be set significantly lower because LOoffset is no longer a factor, in other words subsequent reception has a higher signal to noise for more robust reception.

Mark.
So what you set in registers is 1/2 of that is really going on? Something like +/- FDEV & LOoffset? But LOoffset can be set in positive or negative way. And from what you say AFC is a must and will be much better than setting LOoffset. And with  AFC and good signal, is there any penalty?

perky

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Re: RFM69HW range test!
« Reply #44 on: February 08, 2018, 11:01:14 AM »
So what you set in registers is 1/2 of that is really going on? Something like +/- FDEV & LOoffset? But LOoffset can be set in positive or negative way. And from what you say AFC is a must and will be much better than setting LOoffset. And with  AFC and good signal, is there any penalty?
The benefits of AFC are you can use narrow bandwidths for RxBw to reduce the noise floor and increase transmission distance. Now you could say 'but I have to have a wider RxBwAfc, doesn't that reduce the distance anyway?'. Normally a signal would need to have a certain S/N ratio to get an acceptable bit error rate, but AFC may not need such a high S/N ratio because it is effectively averaging out noise during that period with a known pattern, so the reality is you can do an AFC at a lower signal S/N ratio than the data. Unfortunately this difference isn't documented which is a shame.

The penalty with AFC is the longer preamble needed for the AFC to work, and this can be substantial needing several bytes, maybe up to 5 or more. That has impact on short packet sizes and battery usage.

As for the registers, Fdev sets the deviation from the centre frequency, so a transmitter will transmit at (fc + Fdev) and (Fc - Fdev). RxBw and RxBwAfc are single sideband bandwidths, they set how far out from the receiver's frequency it will receive. In a system where the receiver's centre frequency is the same as the transmitters these are half the full bandwidth of the signal (remember this is a zero IF chip). But if the receiver's centre frequency is offset from the transmitter's, one of those frequencies would be further away from the centre and the other closer. the RxBw would need to be set wider to pull in the furthest transmitted frequency.

Mark.